The invention relates to a device for heating platelike parts made of a deep-drawable plastic material using contact heat and hot gases which are supplied to the part to be heated by means of carrier plates, wherein two carrier plates are movable relative to each other at least vertically to a common contact surface and gas distribution conduits open in the contact surface.
With sintering operations and with this art in general, it is necessary to process platelike parts using a device of the kind mentioned hereinabove, in order to weld or also deep-draw platelike parts made of deep-drawable plastic material. The word "platelike" is used to denote workpieces which are flat or laminar, which are e.g. in the shape of plates, shells, bars, strips or sheets. These kinds of platelike parts made of deep-drawable plastic material are joined together, or are heated by the deep-drawing process. They are placed in contact with so-called carrier plates, so that the heat energy is transmitted from the carrier plates to the platelike workpieces through contact. The idea has also been harbored of applying, alternatingly or additionally, hot gases, preferably hot air, to the platelike workpiece to be heated, in order to improve or accelerate the heating up or warming process. After the heating process, the two oppositely disposed carrier plates which have a common contact surface when they travel together, are displaced relative to each other in such a way that the platelike parts or workpieces can be removed and conveyed to other processing stations.
However, tests have unfortunately revealed that the platelike workpieces to be heated remain stuck to the contact surface, which is flat, for example, of at least one--or two, in the case of particularly bad embodiments--carrier plates. With these tests, gas distribution conduits have now also been arranged in the carrier plates so that the conduits open into the contact surface through openings, with the effect that compressed air can be used in helping to loosen a platelike part. In spite of this feature, the heated platelike workpieces have not always been able to be properly removed from the contact surface of the carrier plate. It has unfortunately been shown, for example, that the injected air for the purpose of pulling off the platelike part or blank from the carrier plate softens at the place where removal has already been effected and then no longer promotes detachment at the other places where there is still strong adhesion between the softened platelike workpiece and the carrier plate. The total air pressure is reduced at said leakage places so that gas distribution conduits are of no use.
Even if the contact surface of the carrier plate is coated with a plastic material, such as for example, Teflon.RTM., removal of the platelike workpiece is not successful in the desired way. It has even been shown in practice that the platelike softened workpiece clings to the layer of Teflon.RTM. and is removed together therewith from the carrier plate by the use of compressed air without the platelike workpiece even being removed properly from the surface as a whole.
The aim of the invention is therefore to create a device of the kind mentioned in the introduction, wherein the platelike parts can be removed properly from the heating plates, so that damage to the heating device can be avoided, and so that the service life of the device can be increased.